The long-term goal of this project is to develop a better understanding of the effects of diminished linguistic experience on language development. The specific model to b tested, termed the 'phonological base hypothesis' (PBH), suggests that children who suffer diminished linguistic experience show delays in phonological development, and that these delays explain delays in language (i.e., syntactic) development. This model evolved from two sources: (1) work by the PI showing a developmental shift in the perceptual weights assigned to acoustic speech parameters and suggesting that this shift is correlated with the development of phonological awareness; and (2) work by others showing that poor phonological awareness is correlated with poor comprehension of complex syntax. An alternative hypothesis to be tested is that children with diminished linguistic experience will show deficiencies in general auditory-processing abilities, and that these deficiencies will explain their delays in language development. Experiments will be conducted with three groups of children thought to suffer diminished linguistic experience (children with histories of chronic otitis media, children from low socioeconomic environments, and hearing-impaired children) and a group of control children. Five Specific Aims will test the hypotheses that children with diminished linguistic experience show delays in the development of mature weighting strategies and in phonological awareness; that delays in the development of these skills result in problems with the comprehension of complex syntax; that early, short-lived deficits in linguistic experience can be overcome, if later experience is adequate and appropriate; that conditions that diminish linguistic experience are additive in their effects; and that delays in phonological or language development are not due to differences in general auditory processing. Results should have implications for the medical and behavioral treatment of children with otitis media, children living in low socioeconomic environments, and hearing-impaired children.